1. Field of the Invention
The field relates generally to media input feed systems for an image forming device (“IFD”) having a removable input tray.
2. Description of the Related Art
IFDs, such as printers, scanners and photocopiers utilize media feed mechanisms for feeding various types of media sheets into the IFDs. Examples of the various types of media sheets include, but are not limited to, printing paper, bond paper, coated paper, fabrics, transparencies and labels. Almost all of the media feed mechanisms include a pick roller that feeds a media sheet into the IFD for further processing. In a media feed mechanism, various arrangements of the pick roller may exist for feeding the media sheet into the IFD.
In one such arrangement of a media feed mechanism, the pick roller may be coupled with other components of the media feed mechanism to exert a normal force on the media sheet. Examples of the other components that may be coupled to the pick roller include solenoids, cams, pick arms, gears, shafts, and the like. Simultaneously, the pick roller may be rotated due to the coupling with the other components to push the media sheet into the IFD due to friction between the pick roller and the media sheet. Herein, pushing the media sheet into the IFD refers to pushing the media sheet in a media process direction into a specific section of the IFD, for example, pushing the media sheet into a ‘printing zone’ where the IFD is a printer.
In existing media feed mechanisms, the normal force, which is applied substantially perpendicular to the flat surface of the media sheet by the pick roller, is generally of a constant value for all types of the media sheets. For example, the pick roller may exert a constant normal force on a bond paper, as well as, a transparency. As is known, media may have different densities, weights, thicknesses and stiffnesses. Further, the normal force required to feed one type of media into the IFD may be greater than the normal force required to feed another type of media. Accordingly, due to the application of the constant normal force on all types of the media sheets in existing media feed mechanisms, multiple feeds or misfeeds of the media sheet may occur.
Further, over time the normal force exerted by the pick roller may decrease due to wear of the pick roller. However, the existing media feed mechanisms may not facilitate increasing the normal force exerted by the pick roller on the media. This limitation may result in replacement of the pick roller in the IFD.
Upon coming in contact with a media sheet, a pick roller applies a normal force (referred to as ‘N’) on the media sheet. Further, there exists a coefficient of friction μ between pick roller and the media sheet. The rotation of the pick roller along with normal force and the coefficient of friction μ result in a driving force in a direction, such that, the media sheet is fed into the IFD. Normal force, the coefficient of friction μ (referred to as ‘μ’) and driving force (referred to as ‘D’) may be related by the following equation:D=μ*N 
As per the relation in the above equation, normal force N is directly proportional to driving force D. It will be evident to a person skilled in the art that a particular value of driving force D drives the media sheet into the IFD. However, it is also evident from the above equation that driving force D also depends upon the coefficient of friction μ, and accordingly any variation in the coefficient of friction μ may vary driving force D. The coefficient of friction (μ) may differ for various types of the media sheet.
It will be evident to a person skilled in the art that based on the relation provided above, the magnitude of normal force N may need to be increased when the coefficient of friction (μ) between the media sheet and a pick roller decreases, in order to maintain the particular value of driving force D required to feed the media sheet in the media processing device. Similarly, the magnitude of normal force N may need to be decreased when the coefficient of friction μ between the media sheet and a pick roller increases, to feed the media sheet in the media processing device.
IFDs typically include multiple input sources to introduce the media sheets into the media path. The input sources may accommodate a range of media types and a range of media sheet quantities from a single media sheet to large quantities such as 2,000 or more sheets. One type of input source is referred to as a removable media input tray (“RMIT”) integrated within the same housing that contains the imaging units of the IFD. A multi-purpose feeder may also be provided on the image forming device housing or as part of the integrated media tray for accommodating a low number of media sheets and often for specialty media sheets that are difficult to feed through normal input trays, such as envelopes, transparencies, and cardstock.
Another input source is referred to as an option assembly typically comprising a housing and a removable media input tray that is slidably received into the option housing. These option assemblies are typically stackable allowing one or more option assemblies to be used with a single image forming device which is typically positioned on top of the uppermost option assembly in the option assembly stack. Typically each option assembly may contain a different type of media such as letterhead or a different size such as A4 or a larger quantity of the same media type that is found in the integrated RMIT.
Each option assembly provides an extension to the media path of the IFD and may provide one or more additional branches or avenues for introducing media into the media path of the IFD. The media path extension extends from the top to the bottom of each option assembly and is upstream of the media path in the IFD. When another option assembly is positioned below an option assembly, the media path extension permits media in the lower option assembly to be fed through the upper option assembly and into the media path of the IFD that extends at its upstream end through the front portion of the integrated media tray. To accomplish the feeding of media either from a RMIT in an option assembly or from another option assembly, feed rollers have been provided in each option housing above the media tray therein and in the media path extension to receive picked media either from a lower option assembly RMIT or from its own adjacent RMIT. One disadvantage of this arrangement is that the feed rollers increase the overall height of each of the option assemblies by 2 cm or more. If a large number of option assemblies are stacked together, this added height may raise the overall height of the image forming system by 10 to 20 cm sometimes requiring a user to choose between removing an option assembly and having to reach to obtain the output of the imaging forming system. It would be advantageous to have a lower height option assembly while still be able to provide for pass-thru media feeding.
With the addition of one or more option assemblies to an IFD, alignment of the media path extension between the various components and to the media path in the IFD becomes problematic due to variations in component tolerances, also known as “tolerance stackup.” Misalignment of the reference surfaces can cause damage to the leading edge of the media or skewing of the media as it moves along the media path extensions and into the IFD. To correct this, alignment reference surfaces against which an edge of the media being fed have been provided in the media trays in the option assemblies. Typically, these reference surfaces are located only in the vicinity of the feed rolls in each option assembly. It would be advantageous to have a reference surface that minimizes this type of misalignment between options trays and between an option tray and the IFD.
Included in each option assembly are a pick mechanism for moving media from the media tray, a media positioning mechanism and one or more drive motors for powering the pick mechanism, media positioning mechanism, and one or more adjustable media restraints such as a side restraint and a rear restraint to accommodate for different media widths and lengths. Further included are media sensors for determining when media is present in the tray, the size of the media and/or the location of the leading and trailing edges of the media.
Most pick mechanisms are designed only for mounting in a single orientation and for feeding media in only a single direction. This is typically achieved through the use of a one-way clutch in the pick mechanism; although other prior art pick mechanisms employ no clutch even though media is fed in a single direction. With both the clutchless and clutched pick mechanisms, their design envisions only a single mode or orientation of mounting. Because an option assembly may be used with more than one type or model of IFD, it would be desirable to have a single pick mechanism that could be mounted in a variety of orientations and provide media feeding in more than one direction.
Conventional pick mechanisms are usually mounted over the media in the media tray on one or more steel rods that extend between the sides of the media tray. With such mounting arrangements it is difficult to remove or repair the pick mechanism and usually requires the intervention of a skilled technician. It would be advantageous if the pick mechanism could be easily removed and reinstalled by a user if repair or replacement were needed. Lastly, conventional pick mechanisms are designed to provide a normal force on the topmost media sheet to be fed that is sufficient to overcome friction with the media sheet immediately beneath. If the rotational direction of these pick mechanisms were reversed, the force would cause the trailing edge of the media sheet to be driven into the rear media restraint damaging the trailing edge. It would be advantageous to have a pick mechanism that could reduce or eliminate such damage.
For media trays that employ elevator or lift plate systems to position media, e.g. to raise the media into a pick position, a single or multiple motors may be used. With prior systems when the media tray was removed for refilling, the user was required to manipulate the media prior to be able to add more. For example, the user had to press down on the media to lower the elevator until caught by a latch. It would be advantageous to have a drive system that could operate both the pick mechanism and the elevator or lift plate with a common motor while also providing the user with a consistent presentation of the media in the media tray when the media tray is removed for refilling. This would reduce manufacturing cost, operating cost and lower weight and energy usage. Further it would be advantageous to utilize a lift plate that reduces the uncertainty in the location of the leading edge of the media as it indexed upward into the picking position.
It would also be advantageous to have a pick mechanism that would reduce the variability in positioning the leading edge of the media. This would allow for the spacing between fed media sheets to be reduced. This is also referred to as “interpage gap.” Reducing interpage gap would increase media throughput without increasing the speed of the system and help to lessen wear and tear.
Media trays have a media dam integrally formed in their front wall that is used to help direct the fed media into the media path. Typically such media dams are at an obtuse angle to the direction of the initial movement of the media being picked. Media dams are known to include wear strips on their front or face. Wear strips are slightly raised surfaces on the front face extending vertically along the surface of the media dam in contact with the picked media and help to decrease friction and aid in corrugating the fed media. Separator rollers are typically provided downstream of the media dam within the housing of the option assembly above the RMIT or in the IFD above the RMIT therein. The separator rollers usually include a pair of opposed rollers forming a nip therebetween driven in the same direction so that one roller stops misfed sheets and the other allows a topmost sheet to be fed. They are used to reduce the chance of media misfeeds such as multiple feeds and shingling. In some instances, separator rollers of one type are changed out to another type depending on media type to be fed from the media tray. Because of their downstream location in the housing, this is at times an awkward process. Further, the location of the separator roller downstream of the media dam outside of the media tray means that for a misfed sheet, there is greater uncertainty in determining the location of the leading edge of the misfed media sheet. It would be advantageous to have a media dam that includes the separator rollers and still further is removably mounted in the media tray so as to be easily uninstalled and reinstalled by a user, to easily change the type and configuration of the separator rolls, and to reduce uncertainty in locating the leading edge of the media sheet of the media to be fed.
Prior pick mechanisms were designed to swing down into the media tray and onto the media stack. This means that the pick mechanism had to be long enough to reach the bottom of the media tray. Also, this means that the overall weight of the pick mechanism would be greater than a system where the pick mechanism does not need to travel to the media tray bottom. A drawback of this arrangement is that when compressible media, such as envelopes or labels having RFID tags, are being fed out of the media tray, the normal force provided by the pick mechanism is greater than needed with the result that the pick mechanism tends to dig into the compressible media further compressing the compressible media which will not separate. Even when an elevator is used to lift the media stack up to the pick mechanism, meaning that the pick mechanism can be shorter and lighter, a similar result occurs. Limiting the travel of the elevator tray does not correct this issue because the end result remains a compliant pick mechanism picking compliant media. In those IFDs where a vertical wall joins the media dam to the bottom of tray, the pick mechanism may compress the media to the point where it then feeds the media directly into the vertical wall thereby prohibiting the media from making it to the inclined media dam portion. For successful compressible media picking to occur, the picking system requires that there be only one compliant element. With both configurations, for normal media, the media and tray or media and elevator are non-compliant elements while the pick mechanism is the compliant element. Whereas for either configuration, when compressible media is present, both the compressible media and the pick mechanism are compliant elements. It would be advantageous to have a pick mechanism that can work reliably with either compressible media or non-compressible media.
In another aspect of media feed systems, determination of the location of the top of the media stack is important. For media elevating trays, when the tray is removed and reinserted, the location of the top of the media stack must be determined. This aids in determining the position of the leading edge of the media sheet that will be fed into the media path. Prior systems use a contact sensor or mechanical gas gauge hardware linkage which references the top of media stack or the lifting plate. It would be advantageous to have a media feed system where such sensors or linkages can be eliminated.